Tissues are structured groups of cells that are specialized to perform a common function necessary for an organism's survival. Every complex animal or plant (multicellular organism) has tissue that organizes and helps to regulate the organism's responses to the environment. The study of tissues is called histology, a term introduced by C. F. Heusinger (1792-1883) in 1822.

Animal tissues include epithelial (skin and digestive), muscular, nervous, connective, and vascular (blood) types. Though it was obvious to early scientists that organisms consist of many types of body parts, they did not possess the technology (such as microscopes) to examine bodily components closely. More importantly, general anatomy was at first a descriptive discipline, based upon obvious characteristics such as the location of organs; no scientist made an effort to classify components according to function or structure. In the 1700s, the term "tissue," from the French tisser, began to be used in...